U.S. patent application number 10/800680 was filed with the patent office on 2005-06-02 for method for fabricating semiconductor optical device.
Invention is credited to Han, Won Seok, Ju, Young Gu, Kim, Jong Hee, Kwon, O Kyun, Park, Sang Hee, Song, Hyun Woo.
Application Number | 20050118741 10/800680 |
Document ID | / |
Family ID | 34464766 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050118741 |
Kind Code |
A1 |
Song, Hyun Woo ; et
al. |
June 2, 2005 |
Method for fabricating semiconductor optical device
Abstract
Provided is a method for fabricating a semiconductor optical
device that can be used as a reflecting semiconductor mirror or an
optical filter, in which two or more types of semiconductor layers
having different etch rates are alternately stacked, at least one
type of semiconductor layers is selectively etched to form an
air-gap structure, and an oxide or a nitride having a good heat
transfer property is deposited so that the air gap is buried,
whereby it is possible to effectively implement the semiconductor
reflector or the optical filter having a high reflectance in a
small period because of the large index contrast between the oxide
or the nitride buried in the air gap and the semiconductor
layer.
Inventors: |
Song, Hyun Woo;
(Daejeon-shi, KR) ; Han, Won Seok; (Daejeon-Shi,
KR) ; Kim, Jong Hee; (Daejeon-Shi, KR) ; Ju,
Young Gu; (Daejeon-Shi, KR) ; Kwon, O Kyun;
(Daejeon-Shi, KR) ; Park, Sang Hee; (Daejeon-Shi,
KR) |
Correspondence
Address: |
JACOBSON HOLMAN PLLC
400 SEVENTH STREET N.W.
SUITE 600
WASHINGTON
DC
20004
US
|
Family ID: |
34464766 |
Appl. No.: |
10/800680 |
Filed: |
March 16, 2004 |
Current U.S.
Class: |
438/39 |
Current CPC
Class: |
H01S 5/18363 20130101;
H01S 5/18308 20130101; H01S 5/02461 20130101; H01S 5/18341
20130101; H01S 5/18305 20130101 |
Class at
Publication: |
438/039 |
International
Class: |
H01L 021/00; H01S
003/08; H01L 021/20 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2003 |
KR |
2003-85359 |
Claims
What is claimed is:
1. A method for fabricating a semiconductor optical device,
comprising the steps of: a. alternately stacking two or more types
of semiconductor layers having different etch rates on a
semiconductor substrate; b. patterning the stacked semiconductor
layers using a given mask; c. forming a mesa structure to etch
selectively at least one type of semiconductor layers resulting in
an air-gap structure, wherein the mesa structure is composed by the
rest of the semiconductor layers; and d. depositing a material
having a good heat transfer property so that the air gap is
buried.
2. The method according to claim 1, wherein the semiconductor
layers stacked in the step b are patterned so that widths of device
regions thereof are narrower than those of supporting regions at
both sides of the device regions.
3. The method according to claim 1, wherein the semiconductor
layers stacked in the step b are patterned so that a width of a
device region thereof is narrower than that of a supporting region
at one side of the device region.
4. The method according to claim 1, wherein the semiconductor
layers are materials that can be grown by a crystalline growth on
the semiconductor substrate.
5. The method according to claim 1, wherein the material having the
good heat transfer property is an oxide, a nitride, or a mixture
thereof.
6. The method according to claim 5, wherein the material having the
good heat transfer property is one of Al.sub.2O.sub.3, ZnO, MgO,
TiO.sub.2, Ta.sub.2O.sub.5, ZrO.sub.2, HfO.sub.2, SiO.sub.2,
Si.sub.3N.sub.4, AlN, and AlON, or a combination thereof.
7. The method according to claim 5, wherein the material having the
good heat transfer property is deposited by an atomic layer
deposition method.
8. The method according to claim 1, wherein the semiconductor
optical device is a reflector or an optical filter.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a semiconductor optical
device applied to a technical field such as an optical
communication device, a surface emitting laser or the like and,
more specifically, to a method for fabricating a semiconductor
optical device that can be used as a semiconductor reflector or an
optical filter.
[0003] 2. Description of the Related Art
[0004] Semiconductor optical devices have been applied to a variety
of fields because of its simple high-density integration and long
life span. The semiconductor optical device having a wavelength
region for communication (i.e., 1.2 .mu.m to 1.8 .mu.m) is mostly
formed on an InP or GaAs substrate. It is possible to obtain the
semiconductor optical device that is available for a reflector or
an optical filter, in case where materials each having high and low
refractive indexes are alternately stacked by each proper
thickness. The aforementioned semiconductor reflector or optical
filter may be applied to active and passive semiconductor devices.
In particular, a highly reflective reflector would be required for
implementing a surface emitting laser, and thus various techniques
have been applied thereto.
[0005] A semiconductor reflector according to a prior art includes
an InP/InAlAs reflector, an InAlGaAs/InAlAs reflector, an
InAlGaAsSb/InAlAsSb reflector, and the like, which are obtained by
lattice-matched growth on an InP substrate [References 1, 5 and 6].
An InP/air-gap reflector has been developed, which can be obtained
by lattice matched growth on an InP substrate and selective etch
[References 3, 4, 7 and 11]. A dielectric reflector obtained by a
deposition method [Reference 2], an Al(Ga)As/GaAs reflector grown
on a GaAs substrate [Reference 12], a reflector obtained by
wet-oxidizing an Al(Ga)As layer on the GaAs substrate [Reference
8], or the like can be attached to a gain medium grown on the InP
substrate using wafer-to-wafer fusion method in order to fabricate
an active device, such as a surface emitting laser.
[0006] [Reference 1]
[0007] Dennis G. Deppe, et al., Vertical cavity surface emitting
lasers with electrically conducting mirrors, U.S. Pat. No.
5,068,868 (Nov. 26, 1991), AT&T Bell Laboratory.
[0008] [Reference 2]
[0009] Jamal Ramdani, et al., Long-wavelength light emitting
vertical cavity surface emitting laser and method of fabrication,
U.S. Pat. No. 6,121,068 (Sep. 19, 2000), Motorola, Inc.
[0010] [Reference 3]
[0011] Chao-Kun Lin, et al., Electrically pumped 1.3 .mu.m VCSELs
with InP/air-gap DBRs., Conference on Lasers and Electro-optics
2002, CPDB10-1, pp. 755.about.757, 2002.
[0012] [Reference 4]
[0013] Chao-Kun Lin, et al., High temperature continuous-wave
operation of 1.3-1.55 .mu.m VCSELs with InP/air-gap DBRs, IEEE 18th
International Semiconductor Laser Conference, ThA6, pp.
145.about.146, 2002.
[0014] [Reference 5]
[0015] I. Sagnes, et al., MOCVD InP/AlGaInAs distributed Bragg
reflector for 1.55 .mu.m VCSELs, Electronics Letters, Vol. 37 (8),
pp. 500.about.501, 2001.
[0016] [Reference 6]
[0017] J. - H. Shin, et al., CW operation and threshold
characteristics of all-monolithic InAlGaAs 1.55 .mu.m VCSELs grown
by MOCVD, IEEE Photonics Technology Letters, Vol. 14 (8), pp.
1031.about.1033, 2002.
[0018] [Reference 7]
[0019] K. Streubel, et al., 1.26 .mu.m vertical cavity laser with
two InP/air-gap reflectors, Vol. 32 (15), pp. 1369.about.1370,
1996.
[0020] [Reference 8]
[0021] H.- E. Shin, et al., High-finesse AlxOy/AlGaAs non-absorbing
optical cavity, Applied Physics Letters, Vol. 72 (18), 1998.
[0022] [Reference 9]
[0023] Sun Jin Yun, et al., Dependence of atomic layer-deposited
Al.sub.2O.sub.3 films characteristics on growth temperature and Al
precursors of Al (CH.sub.3).sub.3 and AlCl.sub.3., J. Vac. Sci. and
Tech., vol 15 (6), pp. 2993.about.2997, 1997.
[0024] [Reference 10]
[0025] Tuomo Suntola, et al., Method and equipment for growing thin
films, U.S. Pat. No. 5,711,811 (Jan. 27, 1998).
[0026] [Reference 11]
[0027] Uchiyama Seiji, "surface light emitting semiconductor laser
device and method for manufacturing thereof", Japanese Patent
Laid-Open No. H11-307863, Furukawa Electric Co. LTD.
[0028] [Reference 12]
[0029] Iwai Norihiro, et al., "surface emitting semiconductor laser
device and its manufacture", Japanese Patent Laid-Open No.
H12-012962, Furukawa Electric Co. LTD.
[0030] However, the above-mentioned conventional semiconductor
reflectors have the following advantages and disadvantages.
[0031] First, the InP/InAlAs reflector, the InAlGaAs/InAlAs
reflector, the InAlGaAsSb/InAlAsSb reflector, and etc., which are
obtained by the lattice-matched growth on the InP substrate, have
an advantage that they are conductive reflectors [Reference 1]
through which a current can be flowed. On the other hand, they have
disadvantages that a growth thickness thereof is large and
thickness adjustment or growth is difficult.
[0032] The InP/air-gap reflector, which can be obtained by the
lattice matched growth on the InP substrate and the selective etch,
has advantages that it has a small thickness and is easily
fabricated while it has a disadvantage that it is mechanically weak
and unstable.
[0033] In the case of dielectric reflector obtained by the
deposition method and the Al(Ga)As/GaAs reflector grown on the GaAs
substrate, and etc., a wafer-to-wafer fusion technique must be
applied thereto. It is known that this technique has a disadvantage
in mass production.
[0034] Further, in the case of the reflector obtained by growing
crystalline thin films on the GaAs substrate and wet-oxidizing an
Al(Ga)As layer of the grown crystal thin film, there is a problem
of poor reliability due to the strain generated at the time of the
wet-oxidizing.
[0035] Therefore, it is required to develop a semiconductor
reflector and an optical filter that are able to overcome the
disadvantages of the conventional semiconductor reflectors, and are
more reliable in structure and easily fabricated.
SUMMARY OF THE INVENTION
[0036] The present invention is directed to a method for
fabricating a semiconductor optical device, which can be used in a
wavelength region for optical communication and be fabricated by
simple processes, and has mechanical reliability and mass
productivity.
[0037] One aspect of the present invention is to provide a method
for fabricating a semiconductor optical device, comprising the
steps of: alternately stacking two or more types of semiconductor
layers having different etch rates on a semiconductor substrate;
patterning the stacked semiconductor layers using a given mask;
forming a mesa structure to etch selectively at least one type of
semiconductor layers resulting in an air-gap structure, wherein the
mesa structure is composed by the rest of the semiconductor layers;
and depositing a material having a good heat transfer property so
that the air gap is buried.
[0038] In a preferred embodiment of the present invention, the
stacked semiconductor layers are patterned so that widths of device
regions thereof are narrower than those of supporting regions at
both sides of the device regions. Alternatively, the stacked
semiconductor layers are patterned so that a width of a device
region thereof is narrower than that of a supporting region at one
side of the device region.
[0039] Here, the semiconductor layers are materials that can be
grown by a crystalline growth on the semiconductor substrate. The
material having the good heat transfer property is an oxide, a
nitride, or a mixture thereof. Preferably, it may be one of
Al.sub.2O.sub.3, ZnO, MgO, TiO.sub.2, Ta.sub.2O.sub.5, ZrO.sub.2,
HfO.sub.2, SiO.sub.2, Si.sub.3N.sub.4, AlN, and AlON, or a
combination thereof, and it can be deposited by an atomic layer
deposition method. In addition, the semiconductor optical device is
a reflector or an optical filter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The above and other features and advantages of the present
invention will become more apparent to those of ordinary skill in
the art by describing in detail preferred embodiments thereof with
reference to the attached drawings in which:
[0041] FIGS. 1A and 1B are perspective views for explaining a
method for fabricating a semiconductor optical device according to
a preferred embodiment of the present invention;
[0042] FIG. 1C is a cross-sectional view taken along the line A1-A2
of FIGS. 1A and 1B;
[0043] FIG. 2 is a cross-sectional view of a semiconductor optical
device according to a preferred embodiment of the present
invention;
[0044] FIG. 3 is a graph illustrating a reflectance property of a
semiconductor optical device according to an embodiment of the
present invention;
[0045] FIG. 4 is a graph illustrating a reflectance spectrum of a
semiconductor optical device according to a preferred embodiment of
the present invention;
[0046] FIG. 5 is a cross-sectional view for explaining an
embodiment in which a upper reflector of a surface emitting laser
is fabricated by applying a method for fabricating a semiconductor
optical device of the present invention; and
[0047] FIG. 6 is a cross-sectional view for explaining an
embodiment in which a lower reflector of a surface emitting laser
is fabricated by applying a method for fabricating a semiconductor
optical device of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0048] The foregoing and other objects and new features of the
present invention will be apparent from the description of this
disclosure and the accompanying drawings.
[0049] Hereinafter, preferred embodiments of the present invention
will be described in detail with reference to the accompanying
drawings. The embodiments of the present invention, however, may be
changed into several other forms, and the scope of the present
invention should not be construed to be limited to the following
embodiments. The embodiments of the present invention are intended
to more completely explain the present invention to those skilled
in the art. Accordingly, the shapes of elements or the like shown
in figures are exaggerated to emphasize distinct explanation, and
elements indicated by like reference numerals in the figures mean
like elements. Further, when it is described that any layer is
present `on` another layer or a semiconductor substrate, it means
that the layer may be present in direct contact with another layer
or the semiconductor substrate. Alternatively, a third layer may be
interposed between them.
[0050] FIGS. 1A and 1B are perspective views for explaining a
method for fabricating a semiconductor optical device according to
a preferred embodiment of the present invention, FIG. 1C is a
cross-sectional view taken along the line A1-A2 of FIGS. 1A and 1B,
and FIG. 2 is a cross-sectional view of a semiconductor optical
device according to an embodiment of the present invention.
[0051] III-V group semiconductor layers 2 and 3 with different etch
rates are alternately and iteratively stacked on an InP
semiconductor substrate 1. At least one type of semiconductor
layers 2 or 3 are selectively etched to form an air gap 5 as in
FIG. 1C, so that a floated bridge (see FIG. 1A) or cantilever (see
FIG. 1B) type of a mesa structure 4 or 9 including the air gap 5 is
formed. At this time, it is noted that the mesa structure 4 and 9
should not be collapsed. In one effective method for the purpose of
this, if the semiconductor layers 2 and 3 are deposited and then
patterned so that the widths of device regions 4a and 9a are
narrower than those of supporting regions 4b and 9b as in FIGS. 1A
and 1B, the remained semiconductor layer 3 in the supporting
regions 4b and 9b will support the remained semiconductor layer 2
in the device regions 4a and 9a since the semiconductor layer 3 in
the supporting regions 4b and 9b remains in part while the
semiconductor layer 3 in the device regions 4a and 9a is completely
etched by lateral selective etching. Besides, the above-mentioned
stable mesa structure 4 may be formed using etching methods with
high selectivity for the III-V group semiconductor layers or using
a method for etching only specific portions of the semiconductor
layers with a mask.
[0052] The semiconductor layers 2 and 3 may be formed by a
metal-organic vapor phase epitaxy method. The materials that can be
grown on the InP substrate 1, such as InP, InGaAs, InAlGaAs, InAlAs
InGaAsP or the like, may be used. Each of the materials can be
subjected to selective etching process having high selectivity by
means of wet etching using a citric acid, phosphoric acid or
hydrochloric acid system.
[0053] Referring to FIG. 2, a material 6 having an excellent heat
transfer property is partially or fully filled into the air gap 5
formed by the etching process as shown in FIG. 1C. At this time,
voids 7 may be partially contained within the air gap 5 in the
process of depositing the material 6. An atomic layer deposition
method may be utilized to effectively fill the material 6 into the
every air gap 5. At this time, using tri methyl aluminum (TMA) and
H.sub.2O as materials enables a dense thin film to be formed with a
refractive index of 1.6 to 1.7 at a relatively low temperature of
about 200 to 400.degree. C.
[0054] For the material 6 having the excellent heat transfer
property, an oxide, a nitride, or a mixture thereof may be used.
For example, Al.sub.2O.sub.3, ZnO, MgO, TiO.sub.2, Ta.sub.2O.sub.5,
ZrO.sub.2, HfO.sub.2, SiO.sub.2, Si.sub.3N.sub.4, AlN, AlON, and
etc. may be used. Alternatively, a combination thereof may be used.
In the case of using an Al.sub.2O.sub.3 thin film, it is possible
to effectively implement a reflector or an optical filter having a
high reflectance even in a small period since it practically has a
significantly different refractive index as compared to those of
semiconductor layers grown on the InP semiconductor substrate 1,
for example, InAlGaAs, InGaAsP, InAlAs, and InGaAs. In addition, a
heat-conductive property is very excellent and accordingly a good
heat release property is obtained, as compared to the semiconductor
layers 2 and 3. When it is applied to an optical device where the
heat release property is critical, it is possible to significantly
enhance the device property of the optical device. Further,
passivation of leakage currents, which may be generated at etched
sections, would be possible when it is applied to an optical active
device. In the Figure, a reference numeral 8 denotes a passage
through which light is incident and reflected.
[0055] As a result, it can be implemented in an InP substrate that
is generally used for light source devices for communication since
the semiconductor layers capable of selectively being etched are
applied, and has a mechanically reliable structure and a good
heat-conductive property due to the material 6 filled in the air
gap 5. As mentioned above, the semiconductor reflector or optical
filter, which is mechanically reliable and has a high reflectance,
may be applied to optical devices, such as a surface emitting
laser, passive optical filter, and etc.
[0056] The semiconductor optical device as described above may be
used as a semiconductor reflector or optical filter. It can be
constructed with a variety of placement and thickness by two or
more different semiconductor layers (e.g., 2 or 3) according to the
design of the optical filter to be used. The optical device
completed by forming basic semiconductor layers and taking the
above processes will have designed optical properties, such as
transmitting or reflecting wavelengths in a specific region, and
the like.
[0057] As a detailed example, the reflectance property as indicated
by the line A of FIG. 3. can be obtained, in the case of designing
a highly reflective reflector at the vicinity of 1.55 .mu.m in
wavelength and fabricating an optical device on the InP substrate
using the above-stated processes.
[0058] FIG. 3 is a graph illustrating a reflectance property as a
change of reflectance versus wavelength, in the semiconductor
optical device according to an embodiment of the present
invention.
[0059] A reflectance spectrum curve (line B) indicates a
reflectance measured at the state where the semiconductor layers 2
and 3 having different etch rates have been alternately and
iteratively stacked on the InP semiconductor substrate 1 as in FIG.
1A or 1B, a reflectance spectrum curve (line C) indicates a
reflectance measured at the state where the air gap 5 has been
formed by selectively etching at least one type of semiconductor
layers 2 or 3 as in FIG. 1C, and a reflectance spectrum curve (line
A) indicates a reflectance measured at the state where an aluminum
oxide film (deletion) has been filled in the air gap 5.
[0060] FIG. 4 is a reflectance spectrum of a semiconductor optical
device according to a preferred embodiment of the present
invention, showing a change in reflectance with a thickness ratio
of the voids 7 contained in an aluminum oxide film (deletion)
filled in the air gap 5. It shows reflectance, in case where the
thickness ratio of the voids 7 within an aluminum oxide film
(Al.sub.2O.sub.3) is 10% (line D) and 5% (line E), and there is no
void (line F).
[0061] FIG. 5 is a cross-sectional view for explaining an
embodiment in which an upper reflector for a surface-emitting laser
is fabricated by applying a method for fabricating a semiconductor
optical device of the present invention.
[0062] A lower reflector 12, a conductive region 13, and a current
confining region 14 are sequentially formed on a semiconductor
substrate 11. The current confining region 14 is formed of a
multi-layer structure of semiconductor layers having different etch
rates. Semiconductor layers 16 having different etch rates are
alternately and iteratively stacked on the current confining region
14 and patterned. At least one type of semiconductor layers are
selectively etched to form air gaps 15 and 17 in the current
confining region 14 and an upper reflector region 22, respectively.
A mesa structure having a bridge or cantilever type floated by the
air gap 17 is formed. A material 18 having an excellent
heat-conductive property is deposited so that the air gaps 15 and
17 are buried, thereby forming a current confining structure in the
current confining region 14. The semiconductor layer 16 and the
filled air gap 17 form the upper reflector 22 having a high
reflectance. Electrodes 19 and 20 are formed on the current
confining region 14 and the conductive region 13, or the substrate
11, respectively. A reference numeral 21 in the figure indicates
output light.
[0063] FIG. 6 is a cross-sectional view for explaining an
embodiment in which a lower reflector for a surface emitting laser
is fabricated by applying a method for fabricating a semiconductor
optical device of the present invention.
[0064] A lower reflector region 40, a conductive region 37, a
current confining region 33 and an upper reflector 34 are
sequentially formed on a semiconductor substrate 31. The lower
reflector region 40 is formed of a multi-layer structure of
semiconductor layers having different etch rates.
[0065] The reflecting semiconductor mirror 34, the current
confining region 33, the conductive region 37 and the lower
reflector region 40 are patterned to form a lower reflector, and
the mesa structure is made by applying the present invention. At
least one type of semiconductor layers is selectively etched so
that an air gap 35 is formed in the lower reflector region 40. The
lower reflector is formed in the lower region 40 of the
semiconductor reflector, by depositing a material 32 having an
excellent heat-conductive property to bury the air gap 35 partially
or fully. Electrodes 36 and 38 are formed on the current confining
region 33 and the conductive region 37, respectively. A reference
numeral 39 in the figure indicates output light.
[0066] As stated above, the method for fabricating the
semiconductor optical device according to the present invention can
be applied to manufacture the upper reflector in the upper
reflector region 22 or the lower reflector of the lower reflector
region 40 in the surface emitting laser shown in FIG. 5 or 6. The
upper reflector and the lower reflector may be simultaneously
fabricated in accordance with the present invention.
[0067] As described above, according to the present invention,
semiconductor layers for a semiconductor reflector or an optical
filter are stacked and then selectively etched to form an air gap,
and one layer or several layers of a material having a good heat
transfer property are deposited on an entire surface of the
semiconductor layer so that the air gap is buried. Accordingly, it
is possible to implement a semiconductor optical device having
mechanical stability, excellent heat-conductive property and
ensured reliability.
[0068] The semiconductor optical device proposed by the present
invention can be applied to a semiconductor reflector, an optical
filter technical field, an optical communication device technical
field, a surface emitting type light source device, a passive
optical device, a semiconductor optical amplifier device, and so
on.
[0069] Although the present invention have been described in detail
with reference to preferred embodiments thereof, it is not limited
to the above embodiments, and several modifications thereof may be
made by those skilled in the art without departing from the
technical spirit of the present invention.
* * * * *